Non-invasive brain stimulations techniques have recently shown promising results in patients with disorders. Notably, transcranial direct current stimulation (tDCS) applied over the left dorsolateral prefrontal cortex has proved to be effective in improving signs of consciousness in about 50% of patients in MCS either after a single stimulation or after repeated sessions. However, brain mechanisms underlying tDCS effects remain poorly understood. Here we aim to assess the effects of prefrontal tDCS on neurophysiological (i.e., electroencephalography - EEG - primary outcome) and behavioral (secondary outcome) measures in severely brain-injured patients with DOC.

Currently, therapeutic options for severely brain-injured patients with disorders of consciousness (DOC), including patients in unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS), are limited and still need to be improved to influence long-term outcomes. Non-invasive brain stimulations (NIBS) techniques have recently shown promising results in DOC. Notably, transcranial direct current stimulation (tDCS) applied over the left dorsolateral prefrontal cortex has proved to be effective in improving signs of consciousness in about 50% of patients in MCS either after a single stimulation or after repeated sessions. However, brain mechanisms underlying tDCS effects remain poorly understood.In the present protocol, the investigators will assess the effects of prefrontal tDCS on neurophysiological (i.e., electroencephalography - EEG - primary outcome) and behavioral (secondary outcome) measures in severely brain-injured patients with DOC in a double-blind sham-controlled design. One anodal and one sham tDCS will be delivered in a randomized order in chronic (>28 days post-onset) severely brain-damaged patients. The stimulation will have an intensity of 2 mA and will last 20 minutes. The anode will be placed on the left dorsolateral prefrontal cortex and the cathode on the right supraorbital region. Ten minutes of high-density EEG will be recorded using a 256-channel saline electrode net (Electrical Geodesics) directly before and after each tDCS session. Behavioral assessments will be performed using the Coma Recovery Scale-Revised before and after each session by an investigator blinded to the treatment allocation.

Inclusion Criteria:

• post-comatose patients
• patients in vegetative state/unresponsive wakefulness syndrome or in minimally conscious state
• patients with stable condition
• patients free of sedative drugs and Na+ or Ca++ blockers (e.g., carbamazepine) or NMDA receptor antagonist (e.g., dextromethorphan)

Exclusion Criteria:

• premorbid neurology antecedent
• patients in coma
• patients < 28 days after the acute brain injury
• patients with a metallic cerebral implant/a shunt
• cranioplasty